Effect of the carboxyl group number of the complexing agent on polishing performance of alumina slurry in sapphire CMP

Alumina abrasive has a high polishing rate in the polishing process, but there are issues that need to be addressed with poor dispersion and poor post-polishing surface quality. This study used complexing agents with various numbers of carboxyl groups to prepare a series of alumina slurries. Scanning electron microscope images and zeta potential analysis demonstrated that the complexing agents could effectively increase the absolute value of alumina particles’ zeta potential and significantly enhance their dispersibility. Additionally, utilizing the UNIPOL-1502 polishing machine, the chemical mechanical polishing (CMP) performance of polishing slurries with complexing agents on sapphire substrates was investigated. According to the findings, as the carboxyl group count rises, material removal initially increases and subsequently declines. The material removal rate using alumina slurry added with complexing agent disodium ethylenediaminetetraacetic acid (the number of carboxyl groups is 4) can reach up to about 4.0 μm/h, which is 52% higher than that without complexing agents, while the average surface roughness of 0.96 nm can be obtained, which is 51% less than that without complexing agents. The X-ray photoelectron spectroscopy results showed that the complexing agents can react with the abrasive particles and sapphire substrates. The friction coefficient test and contact angle test revealed that slurries with complexing agents demonstrated excellent wettability and mechanical action. The sapphire surface becomes smoother as a result of the synergistic effect of chemical etching and mechanical removal.